During the first threesome, you can see in the close-up shot of Erica that she's wearing panties and Larry's feet are on top of the covers. In the wide shot, she is bare from the waste down and his feet are underneath the covers.
The platter that Howard knocks over from the table while trying to untie himself is nowhere to be seen throughout until that shot only.
When Larry and Stan are arguing in the office, Carol at reception is wearing white shoes, but when she goes to tend to Larry after Stan runs away, she is wearing black shoes.
At 64 minutes: When Amelia sees Howard asleep in his wheelchair, he is wearing a Tartan-patterned housecoat, but in subsequent clips his coat is grey.
When Larry gets stabbed, the knife is clearly made of rubber. It can be seen wobbling just after the second stab.
Shadow on Erica's right hand in the opening shot.